Minimizing the corner errors (top and bottom) at optimized cutting rate and surface finish during WEDM of Al6061

Abstract

Aluminum and its alloys specifically Al6061 bear numerous applications in aerospace and marine etc. where dimensional accuracy is of utmost importance which favors the use of wire electric discharge machining (WEDM). However, the achievement of a similar level of dimensional consistency in terms of corner deviation at both upper and the lower face of the workpiece is challenging. The issues of wire lag and wire vibrations are the prime stimuli for provoking the said corner errors, but their influence is notably different at both the faces of the cut specimen. Essentially similar level of corner accuracy is deemed necessary at upper and lower face of the cut specimen for its accurate functionality in its end application. This aspect has not been explicitly studied so far during WEDM of Al6061 alloy which is primarily investigated in this research. Moreover, the aspect of corner accuracy has not been discussed considering the material removal rate and surface roughness to iterate an optimal setting that yields dimensionally consistent product at optimized material removal rate and surface quality which is done herein. Seven WEDM process variables have been selected to envisage their impact on the selected responses under L27 Taguchi’s design. Experimental findings revealed that corner errors realized at top and bottom faces are markedly different. Angular error at the top face is significantly influenced by Wire tension, off-time, and flushing pressure with percentage contributions of 25.5%, 12%, and 15.6% respectively. Whereas, the angular error at bottom is mainly influenced by open voltage, on time, wire feed, and flushing pressure with percentage contribution of 28.5%, 15.3%, 13.2%, and 10.7% correspondingly. In case of surface finish and material removal rate, pulse longevity is the prime control variable with contribution of 51% and 88% respectively. Greater magnitude of wire tension is observed to cause the taperness in the wire electrode that yields higher corner error at the top face. Corner errors at both the faces i.e. top and bottom are reduced at greater value of open voltages. Scanning electron microscopy analysis depicts that the crater depth and its width, material melting, vaporization, and redeposit on the machined surface are increased by increasing spark duration and subsequently poor surface finish is achieved. An optimal parametric combination for simultaneous optimization of the conflicting responses has been proposed using weighted signal-to-noise ratio. The adequacy of the developed optimal combination has also been validated via confirmation trials.